JPH01269921A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To enable normally white display of high contrast and wide angle of field by utilizing the double refraction effect of a liquid crystal display element having negative dielectric anisotropy. CONSTITUTION:The major axis of liquid crystal molecules are perpendicular or nearly perpendicular to glass substrates 9a, 9b when the impressed voltage is off and, therefore, the light transmitting the liquid crystal layer is not subjected to an optical change and the white or transparent display is executed. The major axis of the liquid crystal molecules are oriented horizontal or nearly horizontal with the glass substrates 9a, 9b while the molecules are twisted between the glass substrates when the impressed voltage is on and, therefore, the blue display by the double refraction effect of the light is executed. Namely, the liquid crystal compsn. having the negative dielectric anisotropy is used as a blue mode. The liquid crystal molecules are twisted at 120-360 deg. between the substrates when the voltage is impressed to the liquid crystal compsn. 3 having the negative dielectric anisotropy. The natural pitch of the liquid crystal compsn. 3, designated as p, and the distance between the substrates, designated as d, are specified to a 0.2-2.0d/p range. The normally white display of the high contrast and the wide angle of field is thereby enabled.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a liquid crystal display device, and particularly to a so-called normally white display liquid crystal display device in which the background is bright and the display is dark.

(Prior Art) As the demand for larger display surfaces of liquid crystal display devices increases, twisted nematic type (hereinafter abbreviated as TN type)
Liquid crystal display devices have problems such as insufficient contrast and narrow visual range.

Therefore, as a liquid crystal display device that can replace the TN type liquid crystal display device, the super lysted nemadec type (hereinafter abbreviated as STN type) is described in Japanese Patent Application Laid-Open No. 59-28130.
Liquid crystal display device or super twisted bias effect type birefringence controlled type (SBE)
A type of liquid crystal display device has been proposed and is known.

The structure of an SBE type liquid crystal display device is to place two transparent substrates on which electrodes are formed facing each other with a distance of about 3 to 12 μm between the substrates, and to seal the periphery of the substrates to form a cell. Injected with nematic liquid crystal. As the nematic liquid crystal, cyclohexane liquid crystal, ester liquid crystal, etc., which have positive dielectric anisotropy, are used. A chiral agent is added to this liquid crystal, and the liquid crystal molecular axis is 180 to 36.
The upper and lower substrates are twisted at an angle of 0° (hereinafter referred to as the twist angle). Also, the liquid crystal molecular axis is 5° to the substrate plane.
It has a larger angle of inclination.

Depending on how the polarizing plate is installed, such LCD devices have a yellow mode where a bright yellow display is displayed in the non-selected state and a black display in the selected state, and a blue mode which is deep blue in the non-selected state and transparent in the selected state. It is possible to display it in

In an SBE type liquid crystal display device having such a configuration, the transmitted light changes rapidly with respect to voltage, and even when multi-digit multiplex driving is performed, the contrast is high and the viewing angle is very wide.

(Problem to be Solved by the Invention) Therefore, in order to obtain a liquid crystal display device with a white background that is generally preferable to human eyes, it is necessary to use the above-mentioned blue mode liquid crystal display device and apply a non-selection voltage to the display pixel. but,
It is conceivable to apply a selection voltage to the non-display area pixels. However, in this case, there was a problem in that the liquid crystal portions around each pixel that were not sandwiched between the electrodes were colored blue because no voltage was applied to them.

Furthermore, Japanese Patent Application Laid-open No. 53-102055 discloses a configuration in which a liquid crystal having negative dielectric anisotropy is used and the twist angle is 90' or approximately 90' when a voltage is applied, and the response speed and
Liquid crystal display devices with improved threshold characteristics have been proposed. However, the improvement in threshold characteristics was insufficient, and a major problem remained when multi-digit multiplex driving was performed.

As described above, conventional liquid crystal display devices have problems such as being unable to perform normally white display or having insufficient threshold characteristics.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a liquid crystal display device capable of normally white display, which satisfies contrast, viewing angle, and threshold characteristics.

[Structure of the Invention] (Means for Solving the Problems) The liquid crystal display device of the present invention includes a pair of substrates each having an electrode formed thereon, and is sandwiched between the pair of substrates, and has refraction in the long and short axes of molecules. In a liquid crystal display device having a liquid crystal composition composed of liquid crystal molecules having different ratios, the liquid crystal composition has negative dielectric anisotropy, and when no potential difference is applied between the electrodes, the length of the liquid crystal molecules is The axes are perpendicular or nearly perpendicular to the substrates, and when a potential difference is applied between the electrodes, the long axes of the liquid crystal molecules become horizontal or almost horizontal to the substrates, and the liquid crystal molecules move at an angle of 120° to 360° between the pair of substrates. ′
It has a twisted helical structure, and when the natural pitch of the liquid crystal composition is p and the distance between a pair of substrates is d, d/
It is characterized in that PffiO is in the range of 2 to 2.0.

(Function) When the applied voltage is off, the long axes of the liquid crystal molecules are perpendicular or almost perpendicular to the glass substrate, so the light that passes through the liquid crystal layer undergoes no optical change and produces a white or transparent display. When is on, the liquid crystal molecules are twisted between the glass substrates and their long axes are horizontal or nearly horizontal with respect to the glass substrates, making it possible to display blue color due to the birefringence effect of light. That is, by using a liquid crystal composition having negative dielectric anisotropy in blue mode, it is possible to reproduce a so-called normally white display in which the background is bright and the display is dark.

Furthermore, as a result of various experiments, the present inventors have found that a liquid crystal composition having negative dielectric anisotropy exhibits 12
It can be twisted by 0 to 360 degrees, and when the natural pitch of this liquid crystal composition is p and the distance between the substrates is d, d/P
It has been found that the above objective can be achieved when the is in the range of 0.2 to 2.0. Some of these experiments are shown below.

(Experiment) The following sample was used as a liquid crystal display device, and the contrast, viewing angle, and threshold characteristics were measured when multiplex driving was performed with a time division number of 200 digits.

(Trial, ¥41> After forming a monobasic ROHM forceps layer on a glass substrate on which a transparent electrode was formed, a rubbing treatment was performed.

Then, a pair of glass substrates were aligned so that the rubbing directions matched, a glass fiber spacer was inserted between the glass substrates to control the distance between the substrates to 8 μm, and the periphery was sealed to obtain a liquid crystal cell. In this liquid crystal cell, black dichroic dye S is added to the ester-based nematic liquid crystal having negative dielectric anisotropy.
A cholesteric liquid crystal composition containing 3 wt % of -344 (manufactured by Mitsui Toatsu Co., Ltd.) was injected and sealed. The polarizing plate was installed so that its absorption axis was parallel to the rubbing direction.

(Sample 2) After forming a monobasic Ri-ROM inscription layer on a glass substrate on which a transparent electrode was formed, a rubbing treatment was performed.

Then, a pair of glass substrates were aligned so that the rubbing direction formed 90", a glass fiber spacer was inserted between the glass substrates to control the distance between the substrates to 8 μm, and the periphery was sealed to form a liquid crystal cell. Then, this liquid crystal cell A cholesteric liquid crystal composition similar to that of Sample 1 was injected and sealed, and a polarizing plate was also installed in the same manner.

(Sample 3) After forming a monobasic Ri-ROM inscription layer on a glass substrate on which a transparent electrode was formed, a rubbing treatment was performed.

Then, a pair of glass substrates were aligned so that the rubbing direction made an angle of 120°, a glass fiber spacer was inserted between the glass substrates to control the distance between the substrates to 10 μm, and the periphery was sealed to obtain a liquid crystal cell. In this liquid crystal cell, 3 wt% of black dichroic dye S-344 (manufactured by Mitsui Toatsu Co., Ltd.) was added to the ester-based nematic liquid crystal having negative dielectric anisotropy, and S-811 (manufactured by E. Merck) was added as a chiral agent. d/P
A cholesteric liquid crystal composition mixed therein so as to have a ratio of 0.10 was injected and sealed. The polarizing plate was installed so that its absorption axis was parallel to the rubbing direction.

(Sample 4) A monobasic ROHM forceps layer was formed on a glass substrate on which a transparent electrode was formed, and then subjected to a rubbing treatment.

Then, a pair of glass substrates were aligned so that the rubbing direction made an angle of 120°, a glass fiber spacer was inserted between the glass substrates to control the distance between the substrates to 8 μm, and the periphery was sealed to obtain a liquid crystal cell. Then, in this liquid crystal cell, S-811 (manufactured by E. Merck & Co.) was added as a chiral agent to an ester-based nematic liquid crystal having negative dielectric anisotropy with a d/P of 0.
．． A cholesteric liquid crystal composition mixed therein at a concentration of 25% was injected and sealed. The absorption axis of the polarizing plate was set at an angle of 30° with the rubbing direction.

(Sample 5) A monobasic chromium complex layer was formed on a glass substrate on which a transparent electrode was formed, and then subjected to rubbing treatment.

Then, a pair of glass substrates were aligned so that the rubbing direction made an angle of 120°, a glass fiber spacer was inserted between the glass substrates to control the distance between the substrates to 9 μm, and the periphery was sealed to obtain a liquid crystal cell. Then, in this liquid crystal cell, S-811 (manufactured by E. Merck & Co.) was added as a chiral agent to an ester-based nematic liquid crystal having negative dielectric anisotropy with a d/P of 0.
．． A cholesteric liquid crystal composition mixed with a liquid crystal composition of 75% was injected and sealed. The absorption axis of the polarizing plate was set at an angle of 30' with the rubbing direction.

(Sample 6) A monobasic ROHM forceps layer was formed on a glass substrate on which a transparent electrode was formed, and then rubbed.

Then, a pair of glass substrates were aligned so that the rubbing direction made an angle of 120°, a glass fiber spacer was inserted between the glass substrates to control the distance between the substrates to 9 μm, and the periphery was sealed to obtain a liquid crystal cell. In this liquid crystal cell, black 2
Color dye S-344 (manufactured by Mitsui Toatsu Co., Ltd.) was 3 wt%, and chiral agent S-811 (E., manufactured by Merck & Co., Ltd.) was d/P.
A cholesteric liquid crystal composition mixed in such a manner that the ratio was 2.20 was injected and sealed. The absorption axis of the polarizing plate was set at an angle of 30' with the rubbing direction.

(Sample 7) A monobasic chromium complex layer was formed on a glass substrate on which a transparent electrode was formed, and then rubbed.

Then, a pair of glass substrates were aligned so that the rubbing direction was 270°, a glass fiber spacer was inserted between the glass substrates to control the distance between the substrates to 8 μm, and the periphery was sealed to obtain a liquid crystal cell. In this liquid crystal cell, black 2
Inject a cholesteric liquid crystal composition containing 3 wt% of color dye S-344 (manufactured by Mitsui Toatsu) and S-811 (manufactured by E. Merck) as a chiral agent so that d/P is 0.68. It was sealed. The absorption axis of the polarizing plate was set at an angle of 30'' with the rubbing direction.

(Sample 8) ' A monobasic chromium complex layer was formed on a glass substrate on which a transparent electrode was formed, and then subjected to rubbing treatment.

Then, a pair of glass substrates were aligned so that the rubbing direction was 270°, a glass fiber spacer was inserted between the glass substrates to control the distance between the substrates to 8 μm, and the periphery was sealed to obtain a liquid crystal cell. In this liquid crystal cell, black 2
A cholesteric liquid crystal composition containing 3 wt% of color dye S-344 (manufactured by Mitsui Toatsu) and S-811 (manufactured by E. Merck) as a chiral agent so that d/P was 2.40 was injected. It was sealed. The absorption axis of the polarizing plate was set at an angle parallel to the rubbing direction.

(Sample 9) A monobasic chromium complex layer was formed on a glass substrate on which a transparent electrode was formed, and then rubbed.

Then, a pair of glass substrates were aligned so that the rubbing direction was 300', a glass fiber spacer was inserted between the glass substrates to control the distance between the substrates to 8 μm, and the periphery was sealed to obtain a liquid crystal cell. In this liquid crystal cell, S-811 (manufactured by E. Merck & Co.) was added as a chiral agent to an ester-based nematic liquid crystal having negative dielectric anisotropy with a d/P of 1.
．． A cholesteric liquid crystal composition mixed in at a concentration of 80% was injected and sealed. The absorption axis of the polarizing plate was set at an angle parallel to the rubbing direction.

(Sample 10) A monobasic chromium complex layer was formed on a glass substrate on which a transparent electrode was formed, and then rubbed.

Then, a pair of glass substrates were aligned so that the rubbing direction formed 360°, a glass fiber spacer was inserted between the glass substrates to control the distance between the substrates to 9 μm, and the periphery was sealed to obtain a liquid crystal cell. Then, in this liquid crystal cell, S-811 (manufactured by E. Merck & Co.) was added as a chiral agent to an ester-based nematic liquid crystal having negative dielectric anisotropy with a d/P of 0.
．． A cholesteric liquid crystal composition mixed with a concentration of 15 was injected and sealed. The polarizing plate was installed so that the angle between the absorption axis and the rubbing direction was 30°.

(Sample 11) A monobasic ROHM forceps layer was formed on a glass substrate on which a transparent electrode was formed, and then rubbed.

Then, a pair of glass substrates are aligned so that the rubbing direction forms 360°, and a glass film is placed between the glass substrates.
A liquid crystal cell was prepared by adding Iba Spray 1 No. to control the substrate spacing to 9 μm and sealing the periphery. Then, in this liquid crystal cell, S-811 (manufactured by E. Merck & Co., Ltd.) was added as a chiral agent to the ester-based nematic liquid crystal having negative dielectric anisotropy.
A cholesteric liquid crystal composition mixed so that P was 0.33 was injected and sealed. The polarizing plate was installed so that the angle between the absorption axis of the polarizing plate and the rubbing direction was 30'.

(Sample 12) A monobasic chromium complex layer was formed on a glass substrate on which a transparent electrode was formed, and then rubbed.

Then, a pair of glass substrates were aligned so that the rubbing direction formed 360°, a glass fiber spacer was inserted between the glass substrates to control the distance between the substrates to 8 μm, and the periphery was sealed to obtain a liquid crystal cell. In this liquid crystal cell, black 2
A cholesteric liquid crystal composition containing 3 wt% of a color dye (manufactured by Mitsui Toatsu) and S-811 (manufactured by E. Merck) as a chiral agent at a d/P of 2.20 was injected and sealed. did. The polarizing plate was installed so that its absorption axis was parallel to the rubbing direction.

(Experimental result) Table 1 summarizes the results of the above experiments.

From this table, the sample that obtained practically acceptable results in terms of threshold characteristics, contrast, and viewing angle is sample N.
o, 4.5, 7, 9.11.

What these samples have in common is that the twist angle of the liquid crystal molecules is 120° or more when voltage is applied between the substrates, and d/
P satisfies 0.2 to 2.0.

Sample 1 satisfies the d/P condition, but because the twist angle is small, the applied voltage-transmittance characteristic becomes very dull as shown by curve a in FIG. Similarly, the characteristics of Sample 2 cannot be said to be steep, as shown by the curve in the figure.

On the other hand, in Sample 6 or Sample 7, the twist angle is large and satisfies the line 4'1, but because d/P is large, the applied voltage-transmittance characteristic changes with the applied voltage as shown by curve a in Figure 5. The transmittances do not correspond one-to-one, and hysteresis occurs.

Therefore, when applying a voltage to a cholesteric liquid crystal composition having negative dielectric anisotropy, the twist angle between the substrates is 120 to 36.
By setting d/P in the range of 0.2 to 2.0, the background is bright and the display is dark.
A liquid crystal display device capable of displaying white can be used.

(Example) A preferred example of the present invention will be described below with reference to FIG. This FIG. 1 schematically shows a cross-sectional view of a liquid crystal display device (1).
The region b shows the state of the liquid crystal molecules with a voltage applied between them, and the region b shows the state of the liquid crystal molecules with no voltage applied.

(Specific Example 1) Transparent electrodes (7a) and (7b) of 1-T-0 are formed in the shape of 200 sheets on glass substrates (9a) and (9b). In this way, the transparent electrode (7a),
(7b) is formed on the glass substrate (9a>, (9b
) on which a monobasic Riromoccipital layer (not shown) is formed;
Furthermore, a polyimide film with orientations e (5a) and (5b) is deposited and rubbed. The rubbing direction of these glass substrates (9a) and (9b) is 27
Align the glass substrate (9a) so that it is 0°,
(9b) The distance d is controlled to be 7 μm using a glass fan/iron spacer (not shown), and the periphery is sealed with epoxy resin. Two polarizing plates (lla) are placed on the rough glass substrates (9a) and (9b).
).

As shown in FIG. 2, the glass substrates (9a) and (9b) are each twisted by 30' from the direction of the rubbing process, forming a liquid crystal cell.

In such a liquid crystal cell, a natural pitch p is contained in a bicyclohexane nematic liquid crystal with a birefringence Δn of 0.09.
A chiral agent was mixed so that the
4 (Mitsui Toatsusha's > 3wt%n) was injected into the liquid crystal composition (3) and sealed with a sealant (not shown) consisting of an epoxy adhesive.

The operation of the liquid crystal display device (1) having such a configuration is as follows.
When no voltage is applied, as shown in region b in Figure 1), the long axes of the molecules are aligned with the glass substrate (9a),
Since it is perpendicular or almost perpendicular to (9b), the display is white or transparent. Moreover, when a voltage is applied, liquid crystal molecules move to the glass substrate (9a).

The spiral structure is twisted 270° between (9b) and is horizontal or almost horizontal to the glass substrates (9a) and (91)), so the composite color of blue and black dye due to the birefringence effect of light creates a black color. Normally white display can be performed.

When this liquid crystal display device (1) is multiplex-driven with a time division number of 200 digits, the contrast ratio is as large as about 8, and the viewing angle is 40'' cone, which is sufficient for practical use.

Further, when the vertical axis represents the transmittance and the groove axis represents the applied voltage, as shown by curve a in FIG. 3, the applied voltage-transmittance characteristic was steep and no hysteresis occurred.

(Specific Example 2) The distance d between the glass substrates (9a) and (9b) is 8 μm
The liquid crystal cell of Specific Example 1 has a birefringence Δn of 0.10.
A chiral agent is added to a bicyclohexane-based nematic liquid crystal with a natural pitch p of 11.9 μm (d/P 0.6
8) and the liquid crystal composition (3) mixed therein was injected and sealed. Further, polarizing plates (lla) and (11b) were installed in the same manner as in Example 1 to obtain a liquid crystal display device (1).

In the liquid crystal display device (1) with such a configuration, when the applied voltage is off, the transmittance is very high and the display is white or transparent, and when the applied voltage is on, the display is blue due to the birefringence effect of the liquid crystal molecules. Normal Hora 41 to display the display color.

When this liquid crystal display device (1) was multiplex driven with a time division number of 200 digits, the applied voltage-transmittance characteristic was steep and no hysteresis occurred because dye 1 was not used.

Furthermore, the contrast ratio is approximately 9, which is also very high, and the viewing angle is 30' cone, which is sufficient for practical use.

(Specific Example 3) In the liquid crystal cell of Specific Example 2, a chiral agent was added to the bicyclohexane-based nematic liquid crystal composition with a natural pitch p of 1.
1.1μ77? , (d/P of 0.72), and a liquid crystal composition (3) containing 3 wt % of black dichroic dye was injected and sealed. Furthermore, two polarizing plates (Ila
), (llb (llb)) was installed so that the absorption axes of (llb) were perpendicular to the rubbing direction to obtain a liquid crystal display device (1). At this time, the tilt angle was about 85° with no voltage applied.

In the liquid crystal display device (1) having such a configuration, when the applied voltage is on, a normally white display of black is performed using a composite color of blue and black dye due to the birefringence effect of liquid crystal molecules, and when the applied voltage is on, the display is normally white. White or transparent display can be performed. The applied voltage-transmittance characteristics were steep and no hysteresis occurred.

When this liquid crystal display device is multiplex-driven with a time division number of 2001, the contrast ratio is as large as about 7, and the viewing angle is 50' cone, which is sufficient for practical use.

(Specific Example 4) Silicon monoxide is deposited on glass substrates (9a) and (9b) on which a plurality of transparent electrodes (7a) and (7b) are formed at an angle of 86° from the normal line of the glass substrate to a film thickness of 10 nm. An oblique evaporation layer (not shown) was formed by diagonal vapor deposition, and a monobasic ROM inscription layer (f, not shown) was further formed thereon. The glass substrates (9a) and (9b) are arranged so that the obliquely evaporated layers formed on these glass substrates (9a> and (9b) form an angle of 240° between the substrates, and , (9b) Distance d is 10μI
rL using glass fiber spacers, and the periphery was sealed with epoxy resin to form a liquid crystal cell.

In such a liquid crystal cell, 3 wt% of black dichroic dye S-344 (manufactured by Mitsui Toatsu Co., Ltd.) and S-811 (as a chiral agent) were added to an ester-based nematic liquid crystal having negative dielectric anisotropy.
(manufactured by E. Merck) with a natural pitch p of 10.7μ7
A cholesteric liquid crystal composition (3) mixed so that rL(d/P was >0.75) was injected and sealed.

This liquid crystal display device has a normally white display, and the contrast ratio when multiplexed driving with a time division number of 20017 is approximately 6.8, which is extremely large, and the viewing angle is also large even when multiplexed driving with a 50° cone and multiple phases is performed. It was enough to withstand it.

The specific examples described in detail here are examples of the present invention,
Various types of liquid crystal display devices can be considered as the liquid crystal display device of the present invention.

[Effects of the Invention] Since the present invention utilizes the birefringence effect of a liquid crystal display element having negative dielectric anisotropy, it can provide a liquid crystal display device capable of normally white display with high contrast and a wide viewing angle. can do. In addition, the response speed is sufficiently high that it can also be used with the multi-branch drive of the operator.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view schematically showing a cross section of an embodiment of a liquid crystal display device according to the present invention, and FIG. 2 shows the installation direction of a polarizing plate of a liquid crystal display device according to a specific example of the present invention. Mizonarizu,
Figure 3 shows a specific example of the present invention, transmittance vs. applied voltage ↑(1
FIG. 4 and FIG. 5. (1>...Liquid crystal display device (3)...Liquid crystal composition (9)...Glass substrate (11)...Polarizing plate agent Patent attorney Noriyuki Chika Yudo Kikuo Takehana Figure 1 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] A liquid crystal display device comprising: a pair of substrates each having an electrode formed thereon; and a liquid crystal composition sandwiched between the pair of substrates and comprising liquid crystal molecules having different refractive indexes on the long and short axes of the molecules. wherein the liquid crystal composition has negative dielectric anisotropy, and when no potential difference is applied between the electrodes, the long axis of the liquid crystal molecules is perpendicular or substantially perpendicular to the substrate; When a potential difference is applied between the electrodes, the long axes of the liquid crystal molecules become horizontal or nearly horizontal with respect to the substrates, and the liquid crystal molecules are arranged at an angle of 120° to 360° between the pair of substrates.
° It has a twisted helical structure, and when the natural pitch of the liquid crystal composition is P and the distance between the pair of substrates is d, d/P is in the range of 0.2 to 2.0. Features a liquid crystal display device.